A generic valve of this type in the form of a proportional pressure control valve is disclosed in U.S. Pat. No. 6,286,535 B1. In this known solution, the pump port P in the axial displacement direction of the control piston within the valve housing discharges into the housing. The other two ports in the form of the use port A and the tank port T discharge transversely to the axial direction in the radial direction. The corresponding displacement position of the control piston is into an annulus which on one side adjoins the valve housing and on the other side adjoins the control piston itself. A damping orifice in the control piston permanently connects a damping chamber between the valve housing and the control piston to the annulus. In this way, the transient processes of the control piston can be damped as required with still simultaneously high dynamics for the overall valve. This dampening is necessary when these proportional pressure control valves are used preferably in clutch systems which are used, for example, to connect two shafts, particularly the shafts of machines with transmission shafts.
In the known solution, the connecting channel in the direction of the pilot chamber of the pilot valve with its valve part within the control piston has a throttle. The throttle, on its side facing away from the pilot chamber, is provided with a filter part for filtering out dirt in the fluid stream which otherwise could clog the throttle and could block it in this way. The fluid stream throttled in this way travels with high pressure to a spherical closing or valve part of the pilot valve which can be actuated by a conventional magnetic system, especially a proportional magnetic system. In the process, the fluid stream is routed unbraked after passing through the throttle in the extension of the connecting channel to the spherical valve part. This valve part is spring-loaded against the action of the magnetic system in its closed position along the valve seat of the pilot chamber. The fluid stream routed in this way directly to the valve part applies very high jet forces to the closing element designed to this end to be spherical. This arrangement leads to neutral dynamic effects on the pilot control, and in certain valve states malfunctions are possible. Especially when these valves are being used for hydraulically actuated clutches or the like subject to increased requirements in terms of safety engineering, these malfunctions cannot be tolerated.
In a further development this known generic solution, proportional pressure control valves according to U.S. Pat. No. 5,836,335 are known in which the control piston has a means for limiting pressure spikes, as could easily occur, for example, on the use port A to which hydraulic clutches can be connected. For this purpose, in one preferred embodiment of the known valve, a spring-loaded return valve is inserted into the control piston and clears the fluid-carrying path at a definable pressure threshold value between the annulus and a containing groove permanently connected to the tank port.